Method for producing a marker on a substrate, lithographic apparatus and device manufacturing method

ABSTRACT

A method of producing a marker on a substrate includes projecting a patterned beam on a layer of resist disposed on a substrate in a lithographic apparatus to create a latent marker; and locally heating the substrate at the marker location in the lithographic apparatus to transform the latent marker into a detectable marker.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.10/875,605, filed Jun. 25, 2004, the contents of which are incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to lithographic apparatus and methods.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a target portion of a substrate. Lithographic apparatus can beused, for example, in the manufacture of integrated circuits (ICs). Inthat circumstance, a patterning structure, which is alternativelyreferred to as a mask or a reticle, may be used to generate a circuitpattern corresponding to an individual layer of the IC, and this patterncan be imaged onto a target portion (e.g. including part of, one orseveral dies) on a substrate (e.g. a silicon wafer) that has a layer ofradiation-sensitive material (resist). In general, a single substratewill contain a network of adjacent target portions that are successivelyexposed. Known lithographic apparatus include so-called steppers, inwhich each target portion is irradiated by exposing an entire patternonto the target portion at once, and so-called scanners, in which eachtarget portion is irradiated by scanning the pattern through theprojection beam in a given direction (the “scanning”-direction) whilesynchronously scanning the substrate parallel or anti-parallel to thisdirection.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,liquid-crystal displays (LCDs), thin-film magnetic heads, etc. Theskilled artisan will appreciate that, in the context of such alternativeapplications, any use of the terms “wafer” or “die” herein may beconsidered as synonymous with the more general terms “substrate” or“target portion”, respectively. The substrate referred to herein may beprocessed, before or after exposure, in for example a track (a tool thattypically applies a layer of resist to a substrate and develops theexposed resist) or a metrology or inspection tool. Where applicable, thedisclosure herein may be applied to such and other substrate processingtools. Further, the substrate may be processed more than once, forexample in order to create a multi-layer IC, so that the term substrateused herein may also refer to a substrate that already contains multipleprocessed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of 365, 248, 193, 157 or 126 nm) and extremeultra-violet (EUV) radiation (e.g. having a wavelength in the range of5-20 nm), as well as particle beams, such as ion beams or electronbeams.

The term “patterning structure” used herein should be broadlyinterpreted as referring to a structure that can be used to impart abeam of radiation with a pattern in its cross-section such as to createa pattern in a target portion of the substrate. It should be noted thatthe pattern imparted to the beam of radiation may not exactly correspondto the desired pattern in the target portion of the substrate.Generally, the pattern imparted to the beam of radiation will correspondto a particular functional layer in a device being created in the targetportion, such as an integrated circuit.

A patterning structure may be transmissive or reflective. Examples ofpatterning structures include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions; in this manner, thereflected beam is patterned.

The support structure supports, i.e. bears the weight of, the patterningstructure. It holds the patterning structure in a way depending on theorientation of the patterning structure, the design of the lithographicapparatus, and other conditions, such as for example whether or not thepatterning structure is held in a vacuum environment. The support can beusing mechanical clamping, vacuum, or other clamping techniques, forexample electrostatic clamping under vacuum conditions. The supportstructure may be a frame or a table, for example, which may be fixed ormovable as required and which may ensure that the patterning structureis at a desired position, for example with respect to the projectionsystem. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning structure”.

The term “projection system” used herein should be broadly interpretedas encompassing various types of projection system, including refractiveoptical systems, reflective optical systems, and catadioptric opticalsystems, as appropriate for example for the exposure radiation beingused, or for other factors such as the use of an immersion fluid or theuse of a vacuum. Any use of the term “lens” herein may be considered assynonymous with the more general term “projection system”.

The illumination system may also encompass various types of opticalcomponents, including refractive, reflective, and catadioptric opticalcomponents configured to direct, shape, or control the beam ofradiation, and such components may also be referred to below,collectively or singularly, as a “lens”.

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

The lithographic apparatus may also be of a type wherein the substrateis immersed in a liquid having a relatively high refractive index, e.g.water, so as to fill a space between the final element of the projectionsystem and the substrate. Immersion liquids may also be applied to otherspaces in the lithographic apparatus, for example, between the mask andthe first element of the projection system. Immersion techniques arewell known in the art for increasing the numerical aperture ofprojection systems.

It may be desirable to project the beam of radiation imparted with apattern in its cross-section accurately to the substrate (e.g. withrespect to one or more features or process layers already formed on thesubstrate, or with respect to a predetermined characterization of thesubstrate surface). In such cases, it may be desirable to know therelative position of the substrate with respect to the reticle, in orderto position the substrate in the focal plane of the projection systemthat is located optically between the reticle and the substrate.Therefore, it may be desirable to measure accurately the position of thesubstrate. This measurement may for instance be done by, in anoperation, determining the position of the substrate with respect to thesubstrate table carrying the substrate. In another operation, therelative position of the substrate table is determined with respect tothe reticle. These two measurements together can be used to compute therelative position of the substrate with respect to the reticle. However,it will be understood that several other strategies may be used todetermine the relative position of the reticle with respect to thesubstrate, for instance by directly determining their relative positionor by determining the relative position of the substrate with respect tothe reticle table. It is implicit in these strategies that the positionof the substrate is determined with respect to the position of anotherobject (for example, the substrate table, the reticle table, or thereticle).

Several methods are known to a person skilled in the art to determinethe relative position of a substrate with respect to another object. Forinstance, in case the relative position is determined with respect tothe substrate table, the substrate and the substrate table are bothprovided with alignment markers. The substrate may be provided, forexample, with up to 30 alignment markers. First the positions of some orall of the alignment markers on the substrate and the substrate tableare determined. This procedure may be done by providing an alignmentbeam to a first alignment mark. The first alignment marker is positionedin the alignment beam by moving the substrate table, while monitoringthe position of the substrate table with interferometric devices. Byperforming measurements to the diffraction pattern generated by thealignment marker in combination with the alignment beam, the position ofthe substrate table for which the alignment marker is optimallypositioned with respect to the alignment beam can be determined. Thisoperation may be done for some or all of the alignment markers (on thesubstrate as well as on the substrate table). By comparing the readingsof the interferometric devices monitoring the position of the substratetable that correspond to different positions of the alignment markers,the relative position of the substrate with respect to the substratetable can be determined.

However, any other known method may be used to determine the relativeposition of a substrate with respect to another object. Most of thesealignment techniques use alignment markers provided on the substrate.Therefore, use of such techniques may require that alignment markers areprovided on the substrate. Such measuring markers may be provided to thesubstrate by projecting an alignment marker pattern to a layer of resistprovided on top of the substrate.

After the exposure, the alignment markers are latently present, and thesubstrate is transported out of the lithographic exposure apparatus to aplace where the latent alignment markers can be made visible, i.e. thealignment marker is made detectable for the alignment arrangement used.This is usually done in a track, as will be known to a person skilled inthe art. In such a track, a post exposure bake (PEB) may be carried outin which the substrate is heated to a certain suitable temperature inorder to make the latent alignment marker visible, as will be known to aperson skilled in the art. After this, the substrate may be transportedback into the lithographic apparatus where the alignment markers can beused for determining the relative position of the substrate as describedabove.

Transporting the substrate out of the lithographic apparatus to thetrack, where the latent markers are made visible, and transporting thesubstrate back in to the lithographic apparatus is a time-consumingprocess and therefore reduces the throughput of the system. Thistransportation process may also lead to inaccuracies, since thesubstrate is removed from the substrate table and repositioned on thesubstrate table after treatment in the track. For example, it will beunderstood that the substrate may not be in the exact same position withrespect to the substrate table after repositioning as it was beforeremoval from the substrate table.

SUMMARY

Embodiments of the invention include a method of producing a marker on asubstrate, including projecting a patterned beam on a layer of resistdisposed on a substrate in a lithographic apparatus to create a latentmarker; and locally heating the substrate at the marker location in thelithographic apparatus to transform the latent marker into a detectablemarker.

According to another embodiment of the invention including: providing asubstrate; using the method as described above to produce at least onemarker on the substrate; providing a beam of radiation using anillumination system; aligning said substrate to a patterning structureby using the at least one marker on the substrate; using the patterningstructure to impart the beam with a pattern in its cross-section; andprojecting the patterned beam of radiation onto a target portion of thesubstrate.

In an embodiment of the invention, there is provided a devicemanufacturing method including: using the method mentioned previously toproduce at least one marker on a substrate; aligning the substrate to apatterning structure by using the at least one marker on the substrate;patterning a beam of radiation with a pattern in its cross-section usingthe patterning structure; and projecting the patterned beam of radiationonto a target portion of the substrate.

According to an embodiment of the invention, there is provided alithographic apparatus including: an illumination system for providing abeam of radiation; a support structure for supporting a patterningstructure, the patterning structure serving to impart the beam with apattern in its cross-section; a substrate table for holding a substrate;and a projection system for projecting the patterned beam onto a targetportion of the substrate, wherein the lithographic apparatus includes aninternal device for locally heating the substrate, in order to transforma latent marker on the substrate into a detectable marker.

In another embodiment of the invention, there is provided a lithographicapparatus including: an illumination system configured to provide a beamof radiation; a support structure configured to support a patterningstructure, the patterning structure serving to impart the beam ofradiation with a pattern in its cross-section; a substrate tableconfigured to hold a substrate; a projection system configured toproject the patterned beam onto a target portion of the substrate; andan internal device configured to locally heat the substrate to transforma latent marker on the substrate into a detectable marker.

According to an embodiment of the invention, the device configured tolocally heat the substrate includes a heat generating element, and thelithographic apparatus is configured to bring the heat generatingelement and the latent marker in the vicinity of each other or to pressthe heat generating device and the latent marker against one another.

According to an embodiment of the invention, the lithographic apparatusincludes a device configured to apply electrical energy to the heatgenerating element.

According to an embodiment of the invention, the lithographic apparatusincludes a radiation emitting device configured to provide a radiationbeam to the heat generating element.

According to an embodiment of the invention, the lithographic apparatusincludes a radiation emitting device configured to provide a radiationbeam to the latent marker.

According to an embodiment of the invention, the lithographic apparatusincludes a magnetically device configured to provide an alternatingmagnetic field to the latent marker.

According to an embodiment of the invention, the lithographic apparatusincludes an exhaust device configured to perform suction in the vicinityof the marker.

According to yet another embodiment, there is provided a lithographicapparatus including an illumination system configured to provide a beamof radiation; a support structure configured to support a patterningstructure, the patterning structure serving to impart the beam ofradiation with a pattern in its cross-section; at least one substratetable configured to hold a substrate; a projection system configured toproject the patterned beam onto a target portion of the substrate; andan internal device configured to locally heat the substrate on the atleast one substrate table to transform a latent marker on the substrateinto a detectable marker.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 a, 2 b, 2 c depict a substrate according to an embodiment of theinvention;

FIGS. 3 a, 3 b, 3 c depict a substrate according to an embodiment of theinvention;

FIG. 4 depicts a substrate according to an embodiment of the invention;

FIG. 5 depicts a substrate according to an embodiment of the invention;and

FIG. 6 depicts a substrate according to a further embodiment of theinvention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to anembodiment of the invention. The apparatus includes an illuminationsystem (illuminator) IL configured to provide a beam PB of radiation(e.g. UV radiation or EUV radiation) and a first support structure (e.g.a mask table) MT configured to support a patterning structure (e.g. amask) MA and connected to a first positioning device PM configured toaccurately position the patterning structure with respect to theprojection system (“lens”), item PL. The apparatus also includes asubstrate table (e.g. a wafer table) WT configured to hold a substrate(e.g. a resist-coated wafer) W and connected to a second positioningdevice PW configured to accurately position the substrate with respectto the projection system (“lens”), item PL, the projection system (e.g.a refractive projection lens) PL being configured to image a patternimparted to the beam of radiation PB by a patterning structure MA onto atarget portion C (e.g. including one or more dies) of the substrate W.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above).

The illuminator IL receives a beam of radiation from a radiation sourceSO. The source and the lithographic apparatus may be separate entities,for example when the source is an excimer laser. In such cases, thesource is not considered to form part of the lithographic apparatus andthe radiation beam is passed from the source SO to the illuminator ILwith the aid of a beam delivery system BD including, for example,suitable directing mirrors and/or a beam expander. In other cases thesource may be integral part of the apparatus, for example when thesource is a mercury lamp. The source SO and the illuminator IL, togetherwith the beam delivery system BD if required, may be referred to as aradiation system.

The illuminator IL may include an adjusting structure AM configured toadjust the angular intensity distribution of the beam. Generally, atleast the outer and/or inner radial extent (commonly referred to asσ-outer and σ-inner, respectively) of the intensity distribution in apupil plane of the illuminator can be adjusted. In addition, theilluminator IL generally includes various other components, such as anintegrator IN and a condenser CO. The illuminator includes a conditionedbeam of radiation, referred to as the beam of radiation PB, having adesired uniformity and intensity distribution in its cross-section.

The beam of radiation PB is incident on the mask MA, which is held onthe mask table MT. Having traversed the mask MA, the beam of radiationPB passes through the lens PL, which focuses the beam onto a targetportion C of the substrate W. With the aid of the second positioningdevice PW and position sensor IF (e.g. an interferometric device), thesubstrate table WT can be moved accurately, e.g. so as to positiondifferent target portions C in the path of the beam PB. Similarly, thefirst positioning device PM and another position sensor (which is notexplicitly depicted in FIG. 1) can be used to accurately position themask MA with respect to the path of the beam PB, e.g. after mechanicalretrieval from a mask library, or during a scan. In general, movement ofthe object tables MT and WT will be realized with the aid of along-stroke module (coarse positioning) and a short-stroke module (finepositioning), which form part of the positioning devices PM and PW.However, in the case of a stepper (as opposed to a scanner) the masktable MT may be connected to a short stroke actuator only, or may befixed. Mask MA and substrate W may be aligned using mask alignmentmarkers M1, M2 and substrate alignment markers P1, P2.

The depicted apparatus can be used in the following preferred modes:

1. In step mode, the mask table MT and the substrate table WT are keptessentially stationary, while an entire pattern imparted to the beam ofradiation is projected onto a target portion C at once (i.e. a singlestatic exposure). The substrate table WT is then shifted in the X and/orY direction so that a different target portion C can be exposed. In stepmode, the maximum size of the exposure field limits the size of thetarget portion C imaged in a single static exposure.

2. In scan mode, the mask table MT and the substrate table WT arescanned synchronously while a pattern imparted to the beam of radiationis projected onto a target portion C (i.e. a single dynamic exposure).The velocity and direction of the substrate table WT relative to themask table MT is determined by the (de-)magnification and image reversalcharacteristics of the projection system PL. In scan mode, the maximumsize of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the mask table MT is kept essentially stationaryholding a programmable patterning structure, and the substrate table WTis moved or scanned while a pattern imparted to the beam of radiation isprojected onto a target portion C. In this mode, generally a pulsedradiation source is employed and the programmable patterning structureis updated as required after each movement of the substrate table WT orin between successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning structure, such as a programmable mirror arrayof a type as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

In at least some applications of embodiments of the invention, thelatent alignment markers are made detectable in the lithographicapparatus by performing a local post exposure bake. For example, in someembodiments such an operation may be done at the exposure position. Incase the lithographic apparatus has two or more substrate tables, thisoperation may be done, in other embodiments, at a position remote fromthe exposure position, but inside the lithographic apparatus (e.g. at ameasurement, alignment, or load station).

In order to transform a latent marker into a detectable mark, a localpost exposure bake is performed inside the lithographic apparatus. Bylocally heating the substrate, i.e. at the locations of the latentalignment markers, the latent alignment markers can be made detectablewithout the need for transporting the substrate out of the lithographicapparatus. Also there is no need to remove the substrate W from thesubstrate table WT.

The term “latent marker” used herein broadly refers to a marker whichhas a contrast too low to allow successful and reliable detection of themark. By applying a post exposure bake, the contrast of the latentmarker is increased to allow successful and reliable detection.

Different embodiments of the invention will be described below.

FIGS. 2 a, 2 b and 2 c show an embodiment of the present invention. FIG.2 a shows part of a substrate W with a layer of resist R on top of it.In the layer of resist R a latent alignment marker 10 is provided. Thislatent alignment marker 10 may be provided by projecting an alignmentmarker pattern to the layer of resist R, in a way known to a personskilled in the art. For example, some or all of the rest of the layer ofresist may be masked during this projecting, or may otherwise remainunexposed, such that another pattern may be applied to an unexposed partof the layer of resist e.g. at a later time.

FIG. 2 b shows a heat producing element 20, that is brought in thevicinity of the latent alignment marker 10. The heat producing element20 may be any kind of heat producing element known to a person skilledin the art.

According to an embodiment of the invention, the heat producing element20 may be, for example, a plate (e.g. of platinum) which is connected toa wire 21 (e.g. of silver (Ag)). The dimensions of the heat producingelement 20 are comparable with the latent alignment marker 10, forexample approximately 100 μm-40 μm. However, the heat producing element20 may be slightly smaller than the latent alignment marker (e.g. inorder to prevent unnecessary heating of the resist surrounding thelatent alignment marker 10).

The diameter of the Ag-wire 21 may be larger than the diameter of theheat producing element 20, although this is not shown as such in FIG. 2b. By providing a wire with a relative large diameter with respect tothe heat producing element 20, the heat producing element 20 has arelatively high resistance with respect to the wire and a relativelylarge amount of heat is therefore produced in the heat generatingelement 20, and not in the wire 21. Such a wire is known to a personskilled in the art as a “Wollaston wire.” For example, the wire may beformed as a thin platinum wire with a jacket of silver, wherein thejacket is removed (e.g. etched) from one portion of the wire to form theheat generating element 20.

The Ag-wire is connected to a voltage source VS. Via the Ag-wire 21, avoltage can be applied to the heat producing element 21. This may be,for example, a DC voltage source, an AC voltage source, or apulse-width-modulation (PWM) source. As a result of the voltage applied,a current will flow through the Ag-wire 21 and the heat producingelement 20. It will be understood that the increase of the temperatureis substantially proportional to the applied voltage. The same resultcan be obtained by using a current source.

The heat producing element 20 may be brought in the vicinity of thelatent marker 10. In order to do this the heat producing element 20 maybe connected to a robot arm to move the heat producing element 20 to thedesired position. However, the heat producing element 20 may also bepositioned on a fixed position in the lithographic apparatus. In thatcase, the substrate W may be moved to that fixed position with respectto the heat producing element 20. As the substrate W is positioned on asubstrate table WT that is configured to move, this may be anadvantageous way of bringing the heat generating element 20 close to thelatent marker 10. In an embodiment of the invention, a combination ofthese two embodiments may be used, i.e. the heat producing element 20and the substrate W can both be moved (for example, the heat producingelement 20 may be moved to a fixed position, or may be otherwisecoarsely positioned, with the substrate W being moved to complete thedesired positional relation).

In an embodiment of the invention, the heat producing element 20 mayalso be brought in contact with the latent marker 10. This can beaccomplished by moving the substrate table WT and/or the heat producingelement 20. Care should be taken that the applied pressure does notexceed a predetermined threshold pressure, above which damage may becaused to the layer of resist R. The pressure applied can be monitoredwith one or more pressure sensors (not shown) using, for example, thepositioning device PW for this purpose and/or, e.g., an arm or otherstructure carrying the heat producing element 20.

In principle, the local post exposure bake by the heat producing element20 may cause local deformations in the layer of resist R due to localexpansion, which may result in internal stress in the material. However,it should be noted that the markers are relatively small and may bepositioned outside the target areas C on the substrate W, such thatthese deformations would be relatively harmless. It will also beappreciated that these internal stresses are relatively small and willdisappear after the heated area cools down. The silicon material isfurther known to quickly transport (e.g. diffuse) the heat, i.e. withinmilliseconds.

FIG. 2 c shows a possible result of the post exposure bake. The latentmarker 10 is transformed into a marker 11 that can easily and reliablybe detected by an alignment system. The optical characteristics of thelatent marker 10 are changed and allow detection. The morphology of thelatent marker 10 may have changed as can be seen from FIG. 2 c. In thisexample, the exposed portions are slightly depressed after the localbake.

It will be understood that the local exposure bake can be performedinside the lithographic projection apparatus, and does not need to bedone outside the lithographic projection apparatus. According to anembodiment of the invention, there is no need to remove the substrate Wfrom the substrate table WT, which may increase the accuracy of theprocess. Also, there is no need to transport the substrate W out thelithographic projection apparatus, which may be rather time-consuming.

FIGS. 3 a, 3 b and 3 c schematically depict an alternative embodiment ofthe present invention. According to this embodiment of the invention,the local post exposure bake is carried out by locally heating thelatent alignment marker 10 with a radiation emitting device, such as alaser device 30. FIG. 3 a is similar to FIG. 2 a, depicting a latentmarker 10. FIG. 3 b schematically depicts a laser device 30 thatproduces a laser beam that is projected on the latent marker 10. Thewavelength of the beam generated by the laser 30 should be such that thelaser beam is sufficiently absorbed by the layer of resist R. Thewavelength may therefore be chosen based on the characteristics of thelayer of resist R. In an embodiment of the invention, an (deep) infraredred laser device 30 may be used having, for example, a wavelength of3-10 μm.

Also it may be desirable to choose the intensity of the laser beamcarefully, i.e. it should be high enough to quickly achieve the desiredlocal post exposure bake, but it should not be too high, in order toprevent affecting the resist surrounding the latent marker 10. It may bedesirable to choose the characteristics of the laser beam such thatchemical reaction in the resist surrounding the latent marker 10 isprevented, or at least minimized.

Experiments have shown that laser beams having a wavelength ofapproximately 9,5-10 μm and laser beams having a wavelength ofapproximately 2-3 μm are suitable for performing a local post exposurebake. The required intensity depends on many factors, such as the resistused.

It will be appreciated that embodiments as shown in FIG. 3 may beapplied to provide a quick and accurate local post exposure bake,without the need to physically contact the substrate W.

According to another embodiment, the local post exposure bake is done bylocal induction heating, e.g. by locally applying an alternatingmagnetic field to the latent alignment marker 10. This may be done usinga magnetic device, such as a coil 40, as depicted in FIG. 4. Analternating voltage source VS (or current source) is connected to thecoil 40 via wires 41 and an alternating magnetic field is produced. Theheating process is based on an effect that is similar to the heatingprocess used in microwaves, as will readily be understood by a personskilled in the art.

According to another embodiment, a combination of embodiment 1 and 2 maybe applied, as depicted in FIG. 5. Since it is not always easy toprovide a laser device 30 that produces the desired wavelength that hasthe right characteristics, i.e. enough absorption in the layer of resistR, a heat generating element 50 may be brought in the vicinity or incontact with the latent marker 10. The heat generating element 50 isthen heated by projecting a laser beam upon it, using a laser device 30.One potential advantage of such an alternative is that it may not benecessary to provide wiring 21 to the heat generating element 20 in thevicinity of the latent marker 10. Another potential advantage is ease ofuse with different resists having different characteristics. The laserdevice 30 does not necessarily have to have a wavelength with sufficientabsorption in the layer of resist R, but should have a wavelength tocreate enough absorption by the material of the heat producing element50, of which the material may be chosen freely.

In one embodiment, radiation source SO may be used to heat the heatgenerating element 50. This may simply be done by positioning the heatgenerating element in the focal plane of the radiation source andpositioning the substrate W such that it is in the vicinity of the heatgenerating device 50. In case the local post exposure bake is performedat a remote position, this may also be done by tapping part of theexposure beam generated by the radiation source 50, guide it to theremote position and use it for the local post exposure bake.

As already discussed above, the local heating of the resist may causeoutgassing of the resist. As a result of this, contamination particlesreleased from the resist or otherwise resulting from outgassing maycontaminate the lithographic apparatus and negatively influence itsperformance. In particular, particles that contaminate the projectionlens PL may negatively influence the lithographic apparatus. Therefore,in an embodiment of the invention, the local post exposure bake may beperformed at a position remote from the projection lens PL.

For example, in case a multiple stage machine is used, the stage mayeasily be moved away from the exposure position. In such a multiplestage machine, usually two stations are provided: a measurement stationand an exposure station. At the measurement station, measurements, suchas height measurements, may be performed. Next, the substrate W and thesubstrate table WT are moved to the exposure station, where themeasurements obtained at the measurement station are used (e.g. toposition the substrate with respect to the projection lens). Thisconcept is known to a person skilled in the art.

In order to reduce the negative effects of outgassing and, inparticular, the contamination of the projection lens PL, the local postexposure bake may be performed at one or more positions at themeasurement station. However, it may also be possible to perform thelocal post exposure bake at a different location in the projectionapparatus.

Moving the substrate stage WT and the substrate W away from theprojection lens PL may also be done in a single stage machine.

The negative effects of contamination due to outgassing may also befurther reduced by providing an exhaust device 60, that is arranged toremove contamination particles by suction. FIG. 6 shows an embodiment ofsuch an exhaust device 60 that is provided above the marker 10 that isheated with laser device 30, as already described with reference to FIG.3 b. The strength of suction should be chosen appropriately. If thesuction is too strong, this may negatively influence the flow conditionsin the lithographic apparatus. The suction may be performed during thelocal post exposure bake, but may also be performed or continued afterthe local post exposure bake has been finished. It will be appreciatedthat in use the exhaust device 60 may be positioned in the vicinity ofthe marker.

By locally heating the substrate at the marker location, the marker maybe made detectable for a sensor in a fast way. One potential advantageis that time and energy are not wasted on heating the whole substrate,but only the relevant part of the substrate is heated.

In some applications, the local heating, or local post exposure bake,can easily be performed on the substrate table on which the substrate ispositioned during exposure, and no time is wasted transporting thesubstrate out of the lithographic projection apparatus and removing itfrom the wafer table. No time is wasted transporting the substrate backin the lithographic projection apparatus, positioning it on thesubstrate table. Also, there may be no need in such cases to repositionthe substrate on the substrate table when it is transported back in thelithographic projection apparatus. Such a method may therefore be moreaccurate and less time consuming, and thus may increase the qualityand/or throughput of the system.

A marker has typical dimensions of 100×100 micron, which is a relativelysmall surface area of the substrate, although principles of theinvention may be applied to uses of markers and/or substrates of otherdimensions. Since the local post exposure bake is only applied to thelatent marker, a relatively small amount of contamination particles maypossibly be released due to outgassing of the resist. In order tofurther minimize the risk of contamination particles contaminatinglenses and/or mirrors, the local post exposure bake may be performed ona location remote from such lenses and/or mirrors. In case a multiplestage machine is used, the local post exposure bake may be performed ona position remote from the projection lens.

According to an embodiment, the local heating may be performed byproviding a heat generating element in the vicinity of the latentmarker. This technique may be an easy way of performing a local postexposure bake. It is possible to transport the heat generating elementto the latent marker, but it is also possible to transport the substratetowards the heat generating element.

According to an embodiment, the heat generating element may be pressedagainst the latent marker. This operation may be done in order to ensurea fast and accurate heat transport from the heat generating element tothe latent marker.

According to an embodiment, the heat generating element may be heated byone of applying electrical energy to the heat generating element andprojecting a radiation beam to the heat generating element. Thesetechniques may be easy ways of heating the heat generating element.

According to an embodiment, the local heating may be performed by one ofproviding a radiation beam to the latent marker and providing analternating magnetic field to the latent marker. These techniques may beeasy and accurate ways of directly heating the latent marker.

According to an embodiment, the method further includes performingsuction in the vicinity of the marker. By performing suction,contamination particles may be removed that result from outgassing dueto the local post exposure bake.

While specific embodiments have been described above, it will beappreciated that the invention may be practiced otherwise than asdescribed. In addition, embodiments also include computer programs (e.g.one or more sets or sequences of instructions) to control a lithographicapparatus to perform a method as described herein, and storage media(e.g. disks, semiconductor memory) storing one or more such programs inmachine-readable form. The description is not intended to limit theinvention.

1. A lithographic apparatus comprising: an illumination systemconfigured to condition a beam of radiation; a support structureconfigured to support a patterning structure, the patterning structureserving to impart the beam of radiation with a pattern in the radiationbeam's cross-section; a substrate table configured to hold a substrate;a projection system configured to project the patterned beam onto atarget portion of the substrate; and an internal heat generating devicelocated within the lithographic apparatus and a heat generating portionof the heat generating device being positionable proximate the substrateand operable to locally heat the substrate to transform a latent markeron said substrate into a detectable marker, the internal heat generatingdevice further comprising a heat generating element located within thelithographic apparatus, the heat generating element being heated tocause the local heating of the substrate to transform the latent marker.2. A lithographic apparatus according to claim 1, wherein thelithographic apparatus is configured to bring at least one of the heatgenerating element and the latent marker into the vicinity of the other.3. A lithographic apparatus according to claim 2, wherein thelithographic apparatus comprises a device configured to apply electricalenergy to the heat generating element, thereby heating the heatgenerating element.
 4. A lithographic apparatus according to claim 2,wherein the lithographic apparatus comprises a radiation emitting deviceconfigured to provide a radiation beam to the heat generating element,thereby heating the heat generating element.
 5. A lithographic apparatusaccording to claim 1, wherein the lithographic apparatus comprises anexhaust device configured to perform suction in the vicinity of themarker.
 6. A lithographic apparatus according to claim 1, wherein theapparatus is configured to locally heat the substrate on said at leastone substrate table.
 7. A lithographic apparatus according to claim 6,wherein said at least one substrate table is moveable from a measurementposition to an exposure position and wherein the local heating of saidsubstrate is performed at said measurement position.
 8. A lithographicapparatus as in claim 1, wherein the heat generating element is heatedto a temperature sufficient to effect the local heating of thesubstrate.
 9. A lithographic apparatus comprising: an illuminationsystem configured to condition a beam of radiation; a support structureconfigured to support a patterning structure, the patterning structureserving to impart the beam of radiation with a pattern in the radiationbeam's cross-section; a substrate table configured to hold a substrate;a projection system configured to project the patterned beam onto atarget portion of the substrate; and an internal heat generating devicelocated within the lithographic apparatus and a heat generating portionof the heat generating device being positionable proximate the substrateand operable to locally heat the substrate to transform a latent markeron said substrate into a detectable marker, the internal heat generatingdevice further comprising a heat generating element located within thelithographic apparatus, the heat generating element being heated duringlocal heating of the substrate wherein the internal heat generatingdevice is configured to provide an alternating magnetic field to thelatent marker, thereby inductively heating the latent marker.
 10. Alithographic apparatus comprising: an illumination system configured tocondition a beam of radiation; a support structure configured to supporta patterning structure, the patterning structure serving to impart thebeam of radiation with a pattern in the radiation beam's cross-section;a substrate table configured to hold a substrate; a projection systemconfigured to project the patterned beam onto a target portion of thesubstrate; and an internal heat generating device located within thelithographic apparatus and a heat generating portion of the heatgenerating device being positionable proximate the substrate andoperable to locally heat the substrate to transform a latent marker onsaid substrate into a detectable marker; wherein the internal heatgenerating device further comprises a heat generating element, andwherein the lithographic apparatus is configured to press the heatgenerating element and the latent marker into physical contact with oneanother.